Process of cracking hydrocarbon oil and recovering stabilized distillate



Nov. 1, 1938. P. OSTERGAARD 2,134,926

PROCESS OF CRACKING HYDROCARBON OIL AND RECOVERING STABILIZED DISTILLATE Original Filed Dec. 5, 1935 a vvucm/M Osierzgaanl,

Patented Nov. 1,, 1938 UNITED STATES PATENT OFFICE PROCESS OF CRACKING HYDBOCARBON OIL AND RECOVEBING STABILIZED DIS- TILLATE Povi Ostergaard, Mount Lebanon, Pa... assignor,

by mesne assignments, to Gulf Oil Corporation, Pittsburgh, Pa.,

sylvania a corporation of Penn- 4 Claims.

This invention relates to a process of crackin petroleum oils and particularly to such a process wherein products of the cracking action which boil too low for commercial motor fuel are polymerized or cracked and polymerized in a recycling operation.

The objects of my invention are to convert relatively high boiling petroleum oil into low boiling material useful as motor fuel; to accomplish the aforesaid purpose with minimum production of products boiling below the boiling range of commercial motor fuel; to operate upon such undesirably low boiling material as is produced, to convert it into material within the boiling point range of commercial motor fuel; and to produce a motor fuel of uncommonly high anti-knock characteristics.

In my process, which is a continuous process, I first use the incoming stock as absorbent oil to strip butanes and propanes from the gases leaving the motor fuel condensation zone; the gas enriched charge is then sent to a heating element wherein it is raised to cracking temperature, preferably in the neighborhood of 1030 F.; the products leaving the heating element are immediately quenched with a stream of gas oil and then discharged into a separating zone; vapors from the separating zone are dispatched to a fractionating zone for separation of motor fuel vapors from heavier components; the motor fuel vapors from the fractionating zone are condensed and stabilized; vapors remaining unoondensed after condensation of the motor fuel are scrubbed with incoming stock as above described; condensate from the separating zone is discharged from the system; and condensate from the fractionating zone is partly used for quenching the discharge from the heating element and partly for reflux in the separating zone. In the accompanying drawing I have shown, more or less diagrammatically, one form of apparatus assembly useful in the performance of my process.

The drawing shows an apparatus useful in the performance of my process. A is a tubular heater; of continuous type, situated in a furnace X. B is a separating chamber. C is a fractionating tower. D is a condensing and stabilizing tower comprising an upper condensing section DC, and a lower stabilizing section DS. E is an absorber. F is an accumulator. Trays T are positioned inside of chambers B, C, D, and E, as shown. HI, H2, H3, H4, H5, H6, and H! are heat exchangers. Exchangers H2, H3, H5, H6, and H1 have connections W through which water or other cooling agent may be circulated to and from the exchanger. Heat exchanger H1 is fitted with a trapped drain 22 to keep it free of accumulations of condensate. PI, P2, P3, Pl, P5 and P6 are pumps. The purposes of the various pumps can be readily observed from the drawing and are specifically stated in the description of the process. 9 is a tar cooling coil interposed in tar line 8 which conducts tar out of the system from the bottom of separator B. A recycle connection Ill leads from tar line 8, beyond the cooling coil 9, back to the bottom of separator B, and pump P4 is in this recycle line to effect the desired circulation. Reflux systems RI and R2 provide for refluxing in towers C and D respectively. Reflux system RI on tower C is provided with pump P5 to eifect the desired circulation, and with a heat exchanger H3 to cool the reflux before its return to the tower. Reflux system R2 on tower D is provided with pump P6 to effect the desired circulation, and with a heat exchanger Hi to cool the reflux before its return to the tower. The base of tower D is provided with a liquid level controller l6, and this, by communicating means I'I, operates on valve I8 to maintain a constant level of liquid in the bottom of the tower. Accumulator F is provided with a vent back into tower E to prevent accumulation of gas in the accumulator. In tower C the stream of material taken off for use as reflux is taken from a trapped tray, as shown. In tower D the condensing section DC is separated from stabilizing section DS, but communicates therewith through trap l5. This trap is of the conventional type used in such places, comprising an annulus, with its outer periphery welded to the side walls of the tower and with a hollow cylinder extending upward from its inner periphery. The trap I5 is also provided with an overflow pipe 50, the purpose of which is to allow excess liquid accumulating in the trap l5 to pass into the lower section of the tower. The remaining numbers on the drawing indicate pipe lines, valves, etc. For simplification I have omitted the showing of valves on many lines where their presence isconventional and their necessity and use obvious, as on gas and vapor lines 2, H, M, 2|, 26, etc., and on reflux lines RI, R2. 1 and I3, as well as on other lines.

My process is as follows:

Fresh charging stock such as naphtha as hereinafter described, from line I is forced by Dump Pi through line 2 into the top of absorber E. This stock passes downward through absorber E and out of the bottom thereof through line 3 into accumulator F. In its passage downward through absorber E the stock passes countercurrent to an ascending stream of uncondensed gas from condensing tower D which gas enters the bottom of absorber E through line 2i. Butanes and propanes are extracted from the gas in its passage through the absorber and the residue of the gas, comprising components boiling lower than propanes, passes out of the top of the absorber and out of the system through line 23.

The gas enriched charging stock leaves accumulator F through line 4 and is forced by pump P2 through line 4 and heat exchanger Hi to heater A. The charge is heated to cracking and polymerizing temperatures (of an order hereinafter more specifically stated) in heater A; it is immediately cooled by introduction of quench oil from line 5 and it is pumped through line 6 and heat exchanger HI to the separating chamber B. In heat exchanger HI hot products from the heater A surrender heat to the charge on its way thereto. The heating in heater A will be conducted to bring the material in process to a temperature between 900 F. and 1450" F. and the material during heating will be under a pressure between 500 pounds per square inch and 3000 pounds per square inch. Under these conditions the material entering the system through line I will be cracked, the unsaturated components butylene and propylene will be polymerized to higher boiling point material of high antiknock characteristics, and the butane and propane will be cracked (in varying degrees) to form additional unsaturated compounds to be absorbed in absorber E and returned to heater A for polymerization. When naphtha is charged through line I the cracking of it will increase its antiknock characteristic and the same characteristic will be further increased by the products of the polymerization. Separating chamber B operates under a pressure lower than the pressure in heating tubes A, and the pressure on the material undergoing treatment is reduced at valve 28 at the entrance to separator B. Heating element A comprises a properly designed heating zone with tubes of high heat input and soaking zone with lower heat input. Any conventional heater may be used. The amount of soaking tubes may vary, in accordance with common knowledge of the industry, according to the degree of cracking and polymerization desired on the various products.

In heater A the naphtha charge undergoes a se vere cracking and part of tho butanes and propanes are also cracked. Polymerization of products from the naphtha cracking and from the cracking of butanes and propanes also occurs in heater A. The polymerization is primarily a polymerization of unsaturated hydrocarbons of lighter molecular weight to tar and to gas oil and to gasoline hydrocarbons of higher molecular weight.

The furnace eflluent, together with quench oil, which jointly enter separator B, separates there into liquid and vapor products. Some of the separated vapors are condensed before they escape this chamber due to introduction of reflux into the upper part of the tower from line I. This reflux thoroughly scrubs ascending vapors on trays T. Tarry residuum is withdrawn from separator B through tar connections 8. A tar cooler coil 9 is interposed in tar line 8 and a portion of the tar, after having been cooled, is recirculated to the base of separator B to keep the tar therein below coking temperature.

Uncondensed vapor from separator B passe: through line H to the lower portion of fraction ating tower C and the vapors are fractionated therein to remove all gas oil and other components heavier than motor fuel. Fractionation is assisted by trays T and by a stream of oil taken off a high tray in the tower, cooled in heat exchanger H3, and returned to the top of the tower as reflux by pump P5 and line RI. Additional refluxing can be effected by refluxing some cooled gas oil from the base of this tower C to a tray in the lower portion of the column; this reflux enters the column through line i3. Gas oil and other condensate having boiling points higher than those of motor fuel are removed from the base of tower C through line I2. The hot condensate in line I2, by the aid of pump P3, is first passed as a heating medium through heat exchanger H4 which serves as a reboiler at the base of stabilizing column DS, and is then further cooled in heat exchanger H2. The condensate line l2 branches beyond heat exchanger H2 and reflux lines I and I3 lead from one branch thereof to separator B and to fractionator C respectively, as previously described. The other branch of line I2 conveys excess condensate out of the system when naphtha and other light stock is being introduced through line i as fresh charging stock, but this condensate may be mixed with the incoming charge in line I or line 4 when the charging stock is similar in nature to the condensate from fractionator C.

Uncondensed vapor from fractionator C passes through line l4 to the lower portion of condensing tower DC and the motor fuel vapors are condensed therein by the action of a refluxing stream discharged onto the top tray '1 from the reflux loop R2. This reflux loop R2 conveys condensate from the trap l5 at the bottom of con densing tower DC to a heat exchanger H6, wherein it is cooled by a stream W of water or other convenient cooling medium, and the cooled stream is pumped back into the top of tower DC by pump P6.

Motor fuel condensed in condensing tdwer DC accumulates in the trap l5 at the base of condensing tower DC and overflows onto the top tray of stabilizing tower DS. A pool of motor fuel is accumulated in the base of stabilizing tower DS and is maintained by means of a liquid level controller It. By an actuating means I! this liquid level controller i6 operates on valve ill in line '9 through which line the finished motor fuel leaves the system. Interposed in line I9 are heat exchangers H4 and H5. The motor fuel leaving the base of stabilizing tower DS goes directly to heat exchanger H4 which acts as a reboiler and it is warmed there by indirect heat exchange with hot condensate from the base of fractionator C, as previously described. Any vapors resulting from this warming pass back to stabilizing tower DS through vapor return line a. The stabilized motor fuel from reboiler H4 then passes through line l9 to heat exchanger H5 where it is cooled to storage temperature by indirect heat exchange with water or other adequate cooling agent. From cooler H5 the stabilized and cooled motor fuel proceeds on through line i9 to storage, its rate of flow being controlled by valve ll as previously described.

Gases driven from the motor fuel in stabilizing tower DS pass upward through trap l5 into the condensing tower DC and in turn leave condensing tower DC through line 2| in company with other gases too light to be condensed in condensing tower DC. These gases leaving tower DC through line 2| are principally butanes and propanes and lower boiling gases, with possibly r to give the desired results.

be employed in this process when charging naphans-goes a trace of pentanes and heavier material. They pass from line II through heat exchanger H1 into the bottom of absorber E. In heat exchanger H! the gases are cooled by indirect contact with a flowing stream of water or other cooling agent, and any condensate at this point flows to absorber E through trap 22. In absorber E the gases are absorbed by the incoming charge, as previously described, and if the heat of absorption requires it the absorber is constructed in two or more sections, seriately connected, with intercoolers between. I do not desire to absorb the methane and ethane in absorber E, and so I maintain the conditions therein such asto permit these gases to pass on unabsorbed and they leave the absorber E through line 23 controlled by valve 24. The precise conditions necessary are readily determined from widely published data. In addition to the gas from condensing tower DC I may send gas from other sources to the absorber E and line 26 has been provided for that purpose. If liquefied butanes and propanes are available from other sources these may be charged into accumulator F for thermal treatment with the other charging stock. Valved line 21 has been provided to permit bypassing some of the incoming charge direct to accumulator F without passing it through absorber E.

Straight run naphthas, kerosene, light cracked gas oil, and heavy cracked gas oil, when subiected to the same conditions of temperature and pressure, do not each undergo the same dehee of conversion, and each of them undergoes a degree of conversion quite different from that of butanes and propanes subjected to the same conditions. But any one of these oils together with butanes and propanes in sufllcient quantity, may be cracked simultaneously if the proper recycling rates are maintained on the various components: for instance, butanes and propanes can be cracked to completion in connection with straight run naphtha by employing the proper recycling of butanes and propanes while the naphtha is charged through the heater only once.

This invention produces high octane motor fuels by the simultaneous cracking and polymerization of oils and permanent gases. The permanent gases may be butane, butylene, propane and propylene, and the oils may be straight run naphtha, kerosene, light pressure still furnace feed, or heavy refractory gas oil from stripping pressure still tar. The temperatures and pressures throughout the system are adjusted The temperatures to tha to the unit will be apprErimately as follows: The incoming naphtha charge will enter absorption tower E at a temperature between 40 F. and 120 F. Absorption oi the gases in absorber E will increase the temperature of the incoming stock anywhere from 10 F. to 100 F., and where the temperature so attained is too high I divide absorber E into two sections, seriately arranged, with a cooler between. The temperature at the outlet oi heater A will be maintained at a temperature between 900 F. and 1450 F. Pressure maintained in the tubes of heater A will vary between 500 pounds per square inch and 3000 pounds per square inch. The pressures in separating tower B, fractionating tower C, condensing stabilizing towers DC and D8, and absorber E, will ordinarily be maintained within the range 150 pounds per square inch to 500 pounds per square inch.

When naphtha is being charged to the unit, it

will only be subjected to a single pass cracking,

giving a conversion of the naphtha of 15-75%.

The corresponding conversion of the butanes passed simultaneously through the furnace will be approximately ill-50% and the conversion of the propanes from 5-30%. Hence, only part of the butanes and propanes passed through the furnace will be converted. The remaining butanes and propanes together with the butanes and propanes formed by cracking the naphtha will leave the heating element in an unconverted state for subsequent reabsorbing in absorber E. In this manner a recycling of butanes and propanes from the absorber to the heating element will be effected. The amount of recycling of butanes and propanes from the absorber can be controlled by varying the amount of absorption oil passed to the top of the absorber by by-passing part of the naphtha direct to accumulator F and by varying the pressure on the absorber.

By this process, cracking stocks such as straight run naphtha can be cracked to a much higher degree than is economical at the present time due to reducing the gas loss from this process by rereconverting part of the gaseous hydrocarbons formed by the cracking of naphtha to gasoline and heavier oils. Thereby, a naphtha cracking operation can be carried out to produce gasoline or much higher octane number with higher yields of gasoline than has hitherto been possible.

While naphtha is my preferred charging stock for this process, any other refractory cracking stock can be used, as for example kerosene or light cracked gas oil or heavy cracked recycle stock from the reduction of pressure still tar. With these heavier oils the process may be somewhat modified to include the recycling of part of the unconverted charging stock from the base of the fractionating tower C back to the furnace together with the combined fresh charge and absorbed gases. Also part of the unconverted charging stock may be cooled to 60-l20 F. and used as additional absorption oil along with the fresh charge. The operation with other charging stocks than naphtha is carried out within the temperature and pressure limits specified above.

When I use the term motor fuel" in this application I mean a product having approximately (or better than) the properties specified in the current specifications of the United States Government for motor fuel or airplane fuel; also such as is being currently marketed in the United States for automobile use, as reported in tests published from time to time by the United States Government.

When I use the term naphtha in this application I intend the term to comprehend materials ranging from a motor fuel to any unfinished motor fuel stock which comprises principally components of motor fuel boiling point range.

When I use the term "butanes in this application I mean thereby all of the various saturated and unsaturated hydrocarbons which may be present in the gas and which contain 4 carbon atoms per molecule, and when I use the term "propane I mean thereby all the various saturated and unsaturated hydrocarbons which may be present in the gas and which contain 3 carbon atoms per molecule.

What I claim is:

l. The process of making and recovering sta bilized gasoline of high anti-knock value, which comprises: passing a mixture of hydrocarbon oil and hydrocarbons having 3 to 4 carbon atoms per molecule through a conversion zone wherein the mixture is heated to a temperature effective to crank the oil; passing vaporous and gaseous products of said cracking through a separating and fractionating zone to condense and remove c'onstituents higher boiling than gasoline; passing the thereby fractionated gases and vapors under in elevated pressure and at a temperature substantially above atmospheric directly to a condensing zone, wherein said vapors are refluxed with relatively cool, unstabilized condensate to effect a condensation of further quantities of unstabilized condensate, a portion of said condensate being withdrawn from said zone at a point below the point of introduction of said fractionated gases and vapors, cooled and then returned to the upper part of said zone as a refluxing and condensing medium; delivering a further portion of the unstabilized condensate recovered in said condensing zone to a separate stabilizing zone and therein rectifying it to remove undesirably light constituents therefrom as vapors and to stabilize the remaining gasoline condensate; delivering vapors liberated in said rectification to said condensing zone; withdrawing uncondensed gases and vapors and stabilized gasoline condensate from the upper part of said condensing zone and the lower part of said rectifying zone, respectively; recovering hydrocarbons having 3 to 4 carbon atoms per molecule from said uncondensed gases and vapors; and recycling the thereby recovered hydrocarbons to said conversion zone.

2. The process of making and recovering stabilized gasoline of high anti-knock value, which comprises: passing a mixture of hydrocarbon oil and hydrocarbons having 3 to 4 carbon atoms per molecule through a conversion zone wherein the mixture is heated to a temperature effective to crack the oil; passing vaporous and gaseous products of said cracking through a fractionating zone to condense and remove constituents higher boiling than gasoline; passing the thereby fractionated gases and vapors under an elevated pressure at a temperature substantially above atmospheric directly to a condensing zone, wherein said vapors are refluxed with relatively cool unstabilized condensate to effect a condensation of further quantities of unstabilized condensate, a portion of said condensate being withdrawn from said zone at a point below the point of introduction of said fractionated gases and vapors, cooled and then returned to the upper part of said zone as a refluxing and condensing medium; delivering a further portion of the unstabilized condensate recovered in said condensing zone to a. separate stabilizing zone and rectitying it to remove undesirably light constituents therefrom as vapors and to stabilize the remaining gasoline condensate; delivering vapors liberated in said rectification to said condensing zone; withdrawing uncondensed gases and vapors and stabilized gasoline condensate from the upper part of said condensing zone and the lower part of said rectifying zone, respectively; scrubbing said uncondensed gases and vapors with hydrocarbon oil charging stock to recover hydrocarbons having 3 to 4 carbon atoms per molecule by absorption in said 011, without absorption of substantial quantities of such lower boiling constituents as hydrogen and methane; and delivering the thereby enriched oil to said conversion zone.

3. The process of making and recovering stabilized gasoline of high anti-knock value, which comprises: passing a mixture of naphtha of relatively low anti-knock value and hydrocarbons having 3 to 4 carbon atoms per molecule through a conversion zone wherein the mixture is heated to a temperature of from 900 to 1450? F. to crack said naphtha; passing vaporous and gaseous products of said cracking through a fractionating zone to condense and remove constituents higher boiling than gasoline; passing the thereby fractionated gases and vapors at a temperature substantially above atmospheric to a condensing zone, wherein said vapors are refluxed with relatively cool unstabilized condensate to effect a condensation of further quantitles of unstabilized condensate, a portion of said condensate being withdrawn from said zone at a point below the point of introduction of said fractionated gases and vapors, cooled and then returned to the upper part of said zone as a refluxing and condensing medium; delivering a further portion of the unstabilized condensate from said condensing zone to a separate stabilizing zone and rectifying it to remove undesirably light constituents therefrom as vapors and to stabilize the remaining gasoline condensate; delivering vapors liberated in said rectification to said condensing zone; withdrawing uncondensed gases and vapors and stabilized gasoline condensate from the upper part of said condensing zone and the lower part of said rectifying zone, respectively; scrubbing said uncondensed gases and vapors with naphtha of relatively low antiknock value to recover hydrocarbons having 3 to 4 carbon atoms per molecule by absorption in said naphtha, without absorption of substantial quantities of hydrogen and methane; and delivering the thereby enriched oil to said conversion zone; said cracking being conducted under a superatmospheric pressure of from 500 to 3000 pounds per square inch, and said condensing and rectifying zones being maintained under superatmospheric pressures between and 500 pounds per square inch.

4. The process of making and recovering stabilized gasoline of high anti-knock value, which comprises: passing a mixture of hydrocarbon oil and hydrocarbons having 3 to 4 carbon atoms per molecule through a. conversion zone wherein the mixture is heated to a temperature effective to crack the oil; passing vaporous and gaseous products of said cracking through a separating and fractionating zone to condense and remove constituents higher boiling than gasoline; passing the thereby fractionated gases and vapors under an elevated pressure and at a temperature substantially above atmospheric directly to a. condensing zone, wherein said vapors are refluxed with relatively cool unstabilized condensate to effect a condensation of further quantities of un stabilized condensate, a portion of said condensate being withdrawn from said zone at a. point below the point of introduction of said fractionated gases and vapors, cooled and then returned to the upper part of said zone as a refluxing and condensing medium; delivering a further portion of the unstabilized condensate recovered in said condensing zone to a separate stabilizing zone and therein rectifying it to remove undesirably light constituents therefrom as vapors and to stabilize the remaining gasoline condensate; delivering vapors liberated in said rectification to said condensing zone; withdrawing uncondensed gases and vapors and stabilized gasoline condensate from the upper part of said condensing zone and the lower part of said from 500 to 3000 pounds per square inch, and said fractionating, condensing and rectifying zones being maintained under super-atmospheric pressure between 150 and 500 pounds per square inch. 7

POVL OSTERGAARD.

CERTIF ICA TE 0F CORRECTION Patent No 2, 15LL,926.

November 1, 1958.

POVL OSTERGAARD. It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, first column, line 52-55, for "defree" read degree; line 62, for "100 F." read lOO F.; and second column, line 21;, strike out the syllable "re-";

first column, line 5, claim 1, for the word "crank" read crack; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 20th day of December, A. n: 19 3.

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

from 500 to 3000 pounds per square inch, and said fractionating, condensing and rectifying zones being maintained under super-atmospheric pressure between 150 and 500 pounds per square inch. 7

POVL OSTERGAARD.

CERTIF ICA TE 0F CORRECTION Patent No 2, 15LL,926.

November 1, 1958.

POVL OSTERGAARD. It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, first column, line 52-55, for "defree" read degree; line 62, for "100 F." read lOO F.; and second column, line 21;, strike out the syllable "re-";

first column, line 5, claim 1, for the word "crank" read crack; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 20th day of December, A. n: 19 3.

(Seal) Henry Van Arsdale Acting Commissioner of Patents. 

